1. Field of the Invention
The present invention relates to a data transmission control process in a network system for data transmission among plural communication stations connected to a communication medium, with token passing method.
2. Description of the Prior Art
There has been proposed so-called local area network or LAN, in which plural office equipment such as office computers, word processors, facsimiles etc. are mutually connected by an inexpensive and simple communication network channel, and token passing method is known as a communication control method in such local area network.
In this method, control information or command indicating the transfer of right of communication, called token, is circulated in the network, and a station (hereinafter called node) which has caught the token or has been designated thereby acquires the right of communication. Each node acquires the right of communication and initiates the communication only after receiving the token, and, after the communication, transfers the right of communication by passing the token to a succeeding node (hereinafter called downstream node).
In a data transmission from a node to another node in the local area network, the transmission frame generally contains an address of the destination. In order to determine the address of the destination, each node has to be able to recognize the system structure in the network by some means. Stated differently each node has to recognize the addresses of the nodes present in the network.
For this purpose there has generally been adopted a method of providing the network system with a monitor node for administering the entire system, wherein said monitor node transmits the information on the system structure to other nodes.
In such conventional method, however, many functions are concentrated on the monitor node and the data transmission becomes impossible once it develops a malfunction. In order to avoid such inconvenience, there should be provided substitute means in case of a failure of the monitor node, or some additional means in order to improve the reliability of the system. Besides said method is originally not suitable for a network principally aimed at distributed control, such as LAN. Also the use of a particular monitor node in a small-scale network system inevitably raises the cost of the system.